For many years, green tea has been associated with positive health benefits

Tea drinking is an ancient tradition dating back 5,000 years in China and India. Long regarded in those cultures as an aid to good health, researchers now are studying tea for possible use in the prevention and treatment of a variety of cancers.

All tea comes from the same botanical source, however green tea is processed differently. In green tea, the leaves are not allowed to oxidize but instead are steamed. This process allows the antioxidants including vitamins C, E and polyphenols, and other healthy factors in the leaves to be preserved.

The antioxidants found in tea - called catechins - may selectively inhibit the growth of cancer. In laboratory studies using animals, catechins scavenged oxidants before cell damage occurred, reduced the number and size of tumors, and inhibited the growth of cancer cells. Other types of tea were not nearly as successful as green tea in inhibiting the cancerous cells. In fact, results suggested that green tea was approximately ten times more potent than the other types of tea. Human studies have proven more difficult to quantify, perhaps due to such factors as variances in diet, environment, and genetic population.

1. What are antioxidants?

The human body constantly produces unstable molecules called oxidants, also commonly referred to as free radicals. To become stable, oxidants steal electrons from other molecules and, in the process, damage cell proteins and genetic material. This damage may leave the cell vulnerable to cancer. Antioxidants are substances that allow the human body to scavenge and seize oxidants. Like other antioxidants, the catechins found in tea selectively inhibit specific enzyme activities that lead to cancer. They may also target and repair DNA aberrations caused by oxidants.

2. What levels of antioxidants are found in different teas?

All varieties of tea come from the leaves of a single evergreen plant, Camellia sinensis. All tea leaves are picked, rolled, dried, and heated. When the leaves are allowed to ferment and oxidize, black tea is produced. Because it is less processed, green tea contains higher levels of antioxidants than black tea.

Although tea is consumed in a variety of ways and varies in its chemical makeup, one study showed steeping either green or black tea for about five minutes released over 80 percent of its catechins. Instant iced tea, on the other hand, contains negligible amounts of catechins.

3. What are the laboratory findings?

In the laboratory, studies have shown tea catechins act as powerful inhibitors of cancer growth in several ways: They scavenge oxidants before cell injuries occur, reduce the incidence and size of chemically induced tumors, and inhibit the growth of tumor cells. In studies of liver, skin and stomach cancer, chemically induced tumors were shown to decrease in size in mice that were fed green and black tea.

4. What are the results of human studies?

Although tea has long been identified as an antioxidant in the laboratory, study results involving humans have been contradictory. Some epidemiological studies comparing tea drinkers to non-tea drinkers support the claim that drinking tea prevents cancer; others do not. Dietary, environmental, and population differences may account for these inconsistencies.

Two studies in China, where green tea is a mainstay of the diet, resulted in promising findings. One study involving over 18,000 men found tea drinkers were about half as likely to develop stomach or esophageal cancer as men who drank little tea, even after adjusting for smoking and other health and diet factors A second study at the Beijing Dental Hospital found consuming 3 grams of tea a day, or about 2 cups, along with the application of a tea extract reduced the size and proliferation of leukoplakia, a precancerous oral plaque.

However, a study in the Netherlands did not support these findings. It investigated the link between black tea consumption and the subsequent risk of stomach, colorectal, lung, and breast cancers among 58,279 men and 62,573 women ages 55 to 69. The study took into account such factors as smoking and overall diet. It found no link between tea consumption and protection against cancer.

The National Cancer Institute (NCI) researchers are also investigating the therapeutic use of green tea. One recently completed but unpublished NCI trial studied the antitumor effect of green tea among prostate cancer patients. The 42 patients drank 6 grams of green tea, or about 4 cups, daily for four months. However, only one patient experienced a short-lived improvement, and nearly 70 percent of the group experienced unpleasant side effects such as nausea and diarrhea. The study concluded drinking green tea has limited antitumor benefit for prostate cancer patients.

Although, as mentioned above, there are many contradictory findings about the relative health benefits of green tea, no studies have shown that it is detrimental to one's health. Another popular health trend that's sweeping the nation is organic food. If you want to learn more about organic products, our health experts cover every angle about this health craze.